In a typical electric discharge excited metal vapor laser, the efficiency of the laser is maximized by having only the metal vapor present within the lasing chamber. Even minute amounts of vapor contaminants can affect the laser efficiency. Sometimes unwanted discharges of the laser into the contaminant vapors occur and cause punctures in the walls of the laser. The contamination comes from various sources, such as from impurities in the solid metal used to form the vapor, outgassing from the walls of the laser chamber (typically made of alumina), and leaks through various openings and seals in the laser itself.
To deal with this contamination, some lasers are adapted to utilize the flow of an inert gas, such as neon or argon, through the lasing chamber to purge contaminants therefrom. This is done by having an inlet for the inert gas at one end of the laser and an outlet at the other end attached to a vacuum. Thus, the flow of the inert gas longitudinally through the lasing chamber purges contaminants from within the chamber, however, this also withdraws some of the metal vapor. This longitudinal flow of an inert gas through the lasing chamber thus causes the problem of depleting the metal vapor supply, thus requiring replenishment of the metal vapor more frequently than would otherwise be required. Also, the presence of a flowing inert gas through the lasing chamber could cause discharge of the laser through the gases due to the high voltages in the chamber (usually 50 kv or more) and possibly causing puncturing of the walls of the laser tube. A third problem is that, being that either the inlet or the outlet for the inert gas (usually the inlet) must be at the high voltage end of the laser, it is difficult to design the inlet tubes and gas regulators to have operational lifetimes in such high heat and energy environments commensurate with the other components of the laser.